1. Technical Field of the Invention
The present invention relates generally to commutator motors. More particularly, the invention relates to a commutator motor that utilizes an existing part thereof to restrict radially outward movement of brush holders.
2. Description of the Related Art
Japanese Patent No. 3486094, an English equivalent of which is U.S. Pat. No. 6,005,323, discloses a brush holding device used in a commuter motor.
The brush holding device includes, as shown in FIGS. 10A and 10B, a brush holding frame 110 that holds therein a brush 100, and a base plate 120 on which the brush holding frame 110 is fixed.
The brush holding frame 110 has a box-like shape. The brush holding frame 110 includes a pair of flange portions 111, which respectively protrude from an opposite pair of sides of a bottom plate of the brush holding frame 110, and a protrusion 112 that protrudes downward from the bottom plate.
The base plate 120 has a substantially annular shape. The base plate includes a pair of fixing portions 121, a receiving opening 122, and a movement restricting portion 123. The fixing portions 121 are each cut and raised up from a major surface of the base plate 120 and bent into a hook shape. The receiving opening 122 is formed, by cutting out a rectangular portion of the base plate 120 from the radially outer side to the radially inner side of the base plate 120, to have a substantially “U” shape. The movement restricting portion 123 is provided to restrict the brush holding frame 110 from moving in the radially outward direction of the base plate 120 under the force of a spring (not shown) disposed in the brush holding frame 110.
In the assembly process, the brush holding frame 110 is made to slide radially inward on the major surface of the base plate 120, with the protrusion 112 of the brush holding frame 110 being fitted into the receiving opening 122 of the base plate 120, until the flange portions 111 of the brush holding frame 110 are respectively inserted and fixed in grooves defined by the fixing portions 121 in the base plate 120. Meanwhile, an end surface of the protrusion 112 of the brush holding frame 110 which faces the radial center of the base plate 120 makes contact with the bottom face of the “U”-shaped receiving opening 122 of the base plate 120, so that the radially inward movement of the brush holding frame 110 is restricted by the bottom face of the receiving opening 122. Thereafter, the movement restricting portion 123 is bent up from the major surface of the base plate 120 to make contact with part of the brush holding frame 110, thereby restricting the radially outward movement of the brush holding frame 110.
With the above configuration of the brush holding device, however, it is necessary to bend up the movement restricting portion 123 after attaching the brush holding frame 110 to the base plate 120. Consequently, the number of processes needed to produce the brush holding device is increased, thereby increasing the manufacturing cost.
Moreover, since the radially inward movement of the brush holding frame 110 is restricted by the bottom face of the receiving opening 122 of the base plate 120, it is impossible to push and thereby move the brush holding frame 110 in the radially inward direction when the brush holding device is further assembled to a yoke or an end frame of the commutator motor. Therefore, to prevent interference of the brush holding frame 110 with the yoke or end frame, it is necessary to provide a clearance between the radially outer end of the brush holding frame 110 and the radially inner surface of the yoke or end frame in design of the commutator motor. However, such a clearance will increase the radial dimension of the commutator motor, thus making it difficult to minimize the size of the commutator motor.